1. The Field of the Invention
The field of the invention relates to the extensibility of standardized electrical interconnection schemes such as the PCMCIA interface. The invention also relates to communication systems between a host system and a selectively removable module, such as a PCMCIA card, the communication system operating while the card is electrically connected to the host system. More particularly, the invention relates to infrared communication systems for communicating between entities sharing the same power supply or that are otherwise electrically connected.
2. Present State of the Art
In many instances, host systems, such as computer systems, provide a form of extensibility through the use of modular additions that are typically electrically connected with the host system when added. An example of such modular additions are specialized cards that fit into a PC mother board or PCMCIA cards that fit into a notebook computer PCMCIA receptacle. Such cards are electrically connected to the host system according to a defined interface and typically derive power from the host system in order to operate the circuitry contained therein. The electrical connection further allows communication of data and control information between the two entities.
The defined interface is composed of physical dimensions such as card size, type of electrical contacts, number of electrical contacts, etc. and operating characteristics, such as signals presented on each contact, timing of signals, and/or scheme of operation. Such standardization allows manufacturers other than the host system manufacturer to create the extensible modules for interacting with the host system. Throughout this application, reference will be made to the PCMCIA standard as a representative example and not by way of limitation. The concepts illustrated in connection with the present invention as used with a PCMCIA card can be applied to any standardized interface.
While standards have the advantage of allowing others to successfully interface with the host system, they have limitations that may hamper a card designer. The standards define the number and meaning of electrical connections between the host system and the card and there may be conflict with the objectives of the card designer in accessing facilities found on circuitry within the host system. A standard typically sacrifices some flexibility in order to have the predictability that allows all who design to the standard the ability to interact with the host system. Card designers are sometimes limited in their options since designing to the standard is necessary in order to have a ready market for the card because host system manufacturers will typically support only one or two standards.
Using the PCMCIA standard as a representative example, some of the limitations of a standard will be shown. The PCMCIA standard has defined digital signals (e.g., binary data) and control signals in order to transfer digital information between card and host. The PCMCIA standard does not have facility for analog signals a significant limitation depending on the functionality of a given PCMCIA card.
A representative example throughout this application is that of a speakerphone incorporated on a PCMCIA modem card using a host system microphone and speaker as part of its implementation. Because of such an arrangement, the PCMCIA card requires the analog signal to pass from the microphone to the PCMCIA card and for control thereon before being communicated through the telephone line connector found on the PCMCIA card. Likewise, analog signals will need to be communicated from the PCMCIA modem card to the speaker located on the host system. There needs to be some way to communicate this analog signal between the host system and the PCMCIA card. This particular representative example and the implementation thereof along with the present invention will be shown in more detail hereafter.
Other situations where the host system needs to communicate with the selectively removable card or module in a manner beyond that of the predefined interface include modem DAA cards, data acquisition systems, etc.
It becomes impractical to simply change the standardized interface or omit it altogether in lieu of a custom-designed interface due to the acceptance of standards by host system designers Typically, a host system manufacturer will include one or perhaps two defined interfaces for the interconnection of cards or other extensible modules and if they are not chosen by component manufacturer, there will not be a ready market for the card. It is economically infeasible to attempt to persuade all manufacturers to adopt a custom interface when standards exist that allow most functionality to be implemented therein. It is naturally more desirable to simply extend the existing standard in some fashion in order to accomplish the particular purposes of a selectively removable card or module designer.
Others have attempted to address this extensibility issue and extend a given interface by multiplexing the interface signals, adding additional mechanical and electrical connection arrangements, or by using an external connection between the selectively removable card or module and another connection or interface found and available by the host system through an external cable connecting the two devices. Each of these potential solutions suffer serious detrimental characteristics that lead to a continual search for a better solution.
Multiplexing the signals found on a standardized connection such as the PCMCIA interface uses the same physical or mechanical connection and simply shares the signal band width between the PCMCIA standard protocol and the extension provided by the selectively removable card designer in order to accomplish the desired task. For example, in the representative example of a speakerphone implemented on a modem PCMCIA card, analog voice signals would be mixed with the PCMCIA digital signals in order to transfer voice signals to and from a PCMCIA card (and phone line) and the host system microphone and speaker. The drawbacks encountered include an overburdening of the signals carried on the respective PCMCIA contacts that leads to errors, inefficient operation, and sometimes a performance degradation. Additionally, conflicts may occur with the PCMCIA architecture such that normal communications between the card and the host are sometimes interrupted. Finally, the amount of data communicated between card and host may be insufficient for an application because of the reduction in available band width due to sharing the signals.
Another method of extending the capabilities of an interface is through the use of additional mechanical electrical connections. For example, a side pin can be mounted on the frame of a PCMCIA card for interaction with the corresponding receptacle found within the card guide mounted on the host or other location. Other variations include forms of spring contacts to engage to two metal components, one located on the card frame and the other located on the card guide or otherwise mounted at the host. Such electromechanical connections have been found in many instances to lack solid contact and therefore are less reliable. Furthermore, they are susceptible to increases wear during normal operation because of the location of the electromechanical location. Finally, such a sidepin connection can be very expensive due to the extensive modifications made to the card frame and to the card guide adding additional components.
Many host systems have a variety of different interfaces in order to meet the demands of different communication devices. For example, a PC will have in many instances a sound card having a line out connection or a line in connection in order to handle specifically analog voice signals. A final method of extending the capabilities of a given interface uses external cables to connect the analog data input or output from a sound card to an external connection on the PCMCIA card itself. In this manner, the voice data can be communicated through this external cable and causing no interference with the normal PCMCIA connection. Such an external cable and connector arrangement is cumbersome and unwieldy and requires more physical componentry on the card which in turn increases manufacturing complexity and expense. Furthermore, the external cable or cables are ever present and add to overall desktop clutter. Since a PCMCIA card is used in many instances for use with a portable notebook computer that is set up and taken down often, the additional time and effort for connecting yet another cable is bothersome.
In conclusion, there exists a need for a way of communicating to a selectively removable card that is connected to a host system through a standardized interface that does not use the standardized interface but is also inexpensive, reliable, and convenient for the user of the system and selectively removable card. Though attempts have been made to remedy this problem and allow such communication between host and selectively removable modular card, the drawbacks can be so undesirable as to prohibit actual implementation because of added expense, complexity, and unreliability.